<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>京东输入框</title>
</head>

<body>

    <input type="text">


</body>


<script>
    var a = document.getElementsByTagName('input');

    document.body.addEventListener('keyup', function(e) {

        console.log(e.keyCode);

        if (e.keyCode == 83) {
            a[0].focus();
        }

    });
</script>

</html>